Plural beam electron gun



ug. 30, 1966 w. DIETRICH 3,270,233

PLURAL BEAM ELECTRON GUN Filed Aug. 21, 1962 TTOR NEYS United StatesPatent H 3, 4 Claims. (Cl. 313-69) The present invention relates to anelectron gun and more particularly one which essentially comprises a hotcathode of an annular shape which serves as a source of electron beamsand is provided with an anode, and preferably also with a focusingelectrode.

For heating metals under a high vacuum to the melting point, it isalready known to employ electron beams which are produced by an electronsource consisting of an annular hot cathode which is provided with afocusing electrode. The metal to be melted is usually grounded andserves as an anode for the electrons which are emitted by the hotcathode and are accelerated by this potential distribution toward themetal. Such an annular beam system has, however, the disadvantage that,for example, at the occurrence of gas eruptions from the metal beingmelted, gas discharges may easily occur between the metal and the hotcathode which may soon cause a destruction of the hot cathode.

There is also an annular beam system known in which between the hotcathode which is surrounded by a focusing electrode and the metal to bemelted an anode is provided which is likewise of an annular shape. Themetal is then usually connected to the same electric potential as theanode which is provided along its entire periphery with a continuousslot for the passage of the electrons in the direction toward the metalto be melted. The focusing electrode which surrounds the annular hotcathode is arranged around the latter so that the hot cathode is notvisible from the side of the metal, as seen in the direction of theelectrons passing through the slotted anode. The electrons emerging fromthe hot cathode are deflected by a suitable electric potentialdistribution between the cathode, the focusing electrode and the anode,so that the electrons describe curved paths which start at the hotcathode, extend through the slot of the anode and end on the metal bodyto be melted and have a curvature which decreases in the directiontoward the anode. The slope of this curvature may be varied by asuitable variation of the mentioned potential distribution whereby theangle of impact of the electron rays on the metal body to be melted willalso be changed. The change of the slope of the curves which form thepaths of the electrons and decrease in curvature in the direction towardthe anode is produced by electric fields of different strengths. Whenusing an annular hot cathode, all of the electron rays together form aconical beam the focus of which is located on or near the metal body tobe melted. The hot cathode, the focusing electrode and the continuousslot in the anode of such a known electron gun may, however, also be ofa different than an annular shape. For example, the hot cathode mayconsist of a straight wire, in which case the slot in the anode alsoextends in a straight direction.

An annular electron beam system as above described which has a hotcathode, a focusing electrode, and an anode has, however, considerabledisadvantages in electronoptical and melting respects. The annular shapeof the hot cathode merely permits the emitted electron rays to beelectrically influenced in the radial direction thereof, whereas theelectrons which are emitted from a single point of the hot cathode arescattered very considerably in the tangential direction. This annularbeam system also does not permit the electric fields for focusing theelectron rays upon the metal body to be melted to be replaced bymagnetic fields which are much more suitable from an electronopticalstandpoint and also permit electron beams of a much greater aperturesize to be focused. Furthermore, the continuously slotted anode does notpermit the electron gun to be evacuated independently of the meltingchamber.

It is an object of the present invention to provide an electron gunwhich overcomes the above-mentioned dis advantages and consists of a hotcathode of any desired shape and preferably an annular shape, an anode,and preferably a focusing electrode. According to the invention, theanode is provided with a plurality of adjacent apertures. In addition,magnetic electronoptical means may be provided for influencing thefocusing and/ or changing the direction of the electron beams. Byemploying an anode with a plurality of adjacent apertures, the importantadvantage is attained over an anode with a continuous slot that theelectrons which are emitted from the hot cathode by passing through theseparate apertures are concentrated to form separate electron beamswhereby the tangential scattering losses which are very considerable inan anode with a continuous slot are reduced to a size which is of noconsequence. The anode arrangement according to the invention when madeof an annular shape permits the electron beams to be focused in a radialdirection and/ or to be deflected by conventional magneticelectronoptical means. The electron gun according to the invention doesnot require any electric deflecting means in the accelerating chamberand therefore it also does not require the very complicated andsenistive means which easily get out of adjustment for forming the verycritical electrical deflecting fields. In the electron gun according tothe invention it has been found to be of advantage to provide betweenthe hot cathode and anode a focusing electrode which is associated withthe apertures in the anode and is preferably likewise provided withapertures in axial alignment with those of the anode. This focusingelectrode is supplied with an electric potential which is equal to ormore negative than that of the hot cathode. The flow resistance of theapertures in the anode of the new electron gun to gas molecules whichare contained in the evacuated melting chamber may be made so small thatthe electron gun may be evacuated independently of the evacuation of themelting chamber so that a certain difference in pressure may bemaintained between the melting chamber and the electron gun. Themagnetic deflecting means also serve as an effective ion trap forpreventing ions which are formed in the melting chamber and are flyingin the direction toward the hot cathode from entering the electron gun.

The features and advantages :of the present invention will become moreclearly apparent from the following detailed description of onepreferred embodiment thereof as illustrated diagrammatically in theaccompanying drawings, in which:

FIGURE 1 shows a cross section of a part of an elec tron gun accordingto the invention which is provided with an annular hot cathode, whileFIGURE 2 shows a cross section which is taken along line A-A' in theradial direction of the electron gun according to FIGURE 1.

In the drawings, in which only the essential parts of the electron gunaccording to the invention are shown, this gun comprises a hot cathode 1which is provided with a negative electric potential. The electronswhich are emitted from this hot cathode pass from the latter through theperforated focusing electrode 3 and the apertures in the anode 4 intothe melting chamber 5. The

focusing electrode 3 is provided with an electric potential which isapproximately equal to or more negative than the potential on the hotcathode I, preferably the ground potential. The hot cathode 1 may be ofa type which emits electrons uniformly from its entire surface or it maybe designed so that electrons are emitted only from those parts thereofwhich are located directly above the apertures in the focusingelectrode. This may be attained in a simple manner, for example, bymaking the hot cathode of an alternately thicker and thinner crosssection or by differently activating the different parts of the surfaceof the hot cathode. Underneath the anode 4 electromagnetic means aresecured thereto which consist of coils 6 with fen-- magnetic cores 7.All of these coils 6 preferably have an equal number of windings and areenergized by a current of a constant strength. Of course, some of thecoils may also be provided with a larger number of ampere turns so thatsome of the electron beams 2 may be more strongly deflected than theothers. The cross-sectional size of the magnetic field H which is formedbetween the opposite ends of two adjacent cores 7 is determined by theshape of these ends which may be designed in accordance with theparticular requirements to be fulfilled by the electron gun. It is alsopossible to provide suitable cooling means of a conventional type forcooling the focusing electrode 3, the anode 4, and the electromagneticmeans.

Although the invention has been illustrated and described with referenceto the preferred embodiment thereof, it should be understood that it isin no way limited to the details of such embodiment, but is capable ofnumerous modifications within the scope of the appended claims. Thus,for example, the hot cathode, anode, and focusing electrode do not haveto be of an annular shape, but these elements may also be made of adifferent shape to suit the particular purpose for which the electrongun is to be used. The hot cathode may be made, for example, in the formof a straight wire and the focusing electrode and anode also be providedwith apertures which extend in a straight line. The apertures in thefocusing electrode and anode may also be made of any desired shape andsome of the adjacent apertures may also differ from each other both insize and shape. Furthermore, the associated apertures in the focusingelectrode and in the anode may also differ from each other in size andshape.

Having thus fully disclosed the invention, what I claim 1. In anelectron gun comprising a hot cathode, an anode having a plurality ofapertures laterally adjacent but spaced from each other at one side ofsaid hot cathode, a focusing electrode interposed between said hotcathode and said anode, said electrode having a plurality of aperturessubstantially in axial alignment with the corresponding apertures insaid anode for passing separate electron beams from said hot cathodethrough the different aligned apertures, and a plurality ofelectromagnets at the other side of said anode each having a coil and aferromagnetic core, the opposite ends of adjacent cores being spacedfrom each other to form gaps substantially in alignment with saidapertures for forming magnetic fields for independently deflecting eachof said electron beams passing through said apertures in said focusingelectrode and anode and then through said gaps.

2. In an electron gun comprising a hot cathode, an anode having aplurality of apertures laterally adjacent but spaced from each other atone side of said hot cathode, a focusing electrode interposed betweensaid hot cathode and said anode, said electrode having a plurality ofapertures substantially in axial alignment with the correspondingapertures in said anode for passing separate electron beams from saidhot cathode through the different aligned apertures, and a plurality ofelectromagnets at the other side of said anode each having a coil and aferromagnetic core, said coils having an equal number of windings andadapted to be energized by a current of the same strength, the oppositeends of adjacent cores being spaced from each other to form gapssubstantially in alignment with said apertures for forming magneticfields for individually deflecting each of said electron beams passingthrough said apertures in said focusing electrode and anode and thenthrough said gaps.

3. In an electron gun comprising a hot cathode, an anode having aplurality of apertures laterally adjacent but spaced from each other atone side of said hot cathode, a focusing electrode interposed betweensaid hot cathode and said anode and, said electrode having a pluralityof apertures substantially in axial alignment with the correspondingapertures in said anode for passing separate electron beams from saidhot cathode through the different aligned apertures, and a plurality ofelectromagnets at the other side of said anode, each of saidelectromagnets having a coil and a ferromagnetic core, at least one ofsaid coils having a number of windings different from the number ofwindings of the other coils and adapted to be energized by a current ofa different strength than the current for energizing the other coils,the opposite ends of adjacent cores being spaced from each other to formgaps substantially in alignment with said apertures for forming magneticfields for individually deflecting each of said electron beams passingthrough said apertures in said focusing electrode and anode and thenthrough said gaps.

4. In an electron gun comprising a hot cathode, an anode having aplurality of apertures laterally adjacent but spaced from each other atone side of said hot cathode, a focusing electrode interposed betweensaid hot cathode and said anode and, said electrode having a pluralityof apertures substantially in axial alignment with the correspondingapertures in said anode for passing separate electron beams from saidhot cathode through the different aligned apertures, and a plurality ofelectromagnets at the other side of said anode, each of saidelectromagnets having a coil and a ferromagnetic core, at least one ofsaid coils having a number of windings different from the number ofwindings of the other coils and adapted to be energized by a current ofa different strength that the current for energizing the other coils,the opposite ends of adjacent cores being spaced from each other to formgaps substantially in alignment with said apertures for forming magneticfields for individually deflecting each of said electron beams passingthrough said apertures in said focusing electrode and anode and thenthrough said gaps, said opposite ends of said adjacent cores havingsurfaces of a particular shape adapted to determine the cross-sectionalshape of said magnetic fields.

References Cited by the Examiner UNITED STATES PATENTS 2,083,203 6/1937Schlesinger 31382.1 X 2,660,612 11/1953 Wood 315-13 X 2,690,517 9/1954Nicoll et al. 31382.1 X 2,743,389 4/1956 Giuffrida 3l5l3 2,757,3137/1956 Miller 315-13 2,758,234 8/1956 Hensel 313-82.1 X 3,040,112 6/1962Smith 31382 X 3,068,309 12/1962 Hanks.

DAVID J. GALVIN, Primary Examiner.

GEORGE N. WESTBY, ARTHUR GAUSS, Examiners.

C. O. GARDNER, V. LAFRANCHI, R. SEGAL,

Assistant Examiners.

1. IN AN ELECTRON GUN COMPRISING A HOT CATHODE, AN ANODE HAVING APLURALITY OF APERTURES LATERALLY ADJACENT BUT SPACED FROM EACH OTHER ATONE SIDE OF SAID HOT CATHODE, A FOCUSING ELECTRODE INTERPOSED BETWEENSAID HOT CATHODE AND SAID ANODE, SAID ELECTRODE HAVING A PLURALITY OFAPERTURES SUBSTANTIALLY IN AXIAL ALIGNMENT WITH THE CORRESPONDINGAPERTURES IN SAID ANODE FOR PASSING SEPARATE ELECTRON BEAMS FROM SAIDHOT CATHODE THROUGH THE DIFFERENT ALIGNED APERTURES, AND A PLURALITY OFELECTROMAGNETS AT THE OTHER SIDE OF SAID ANODE EACH HAVING A COIL AND AFERROMAGNETIC CORE, THE OPPOSITE ENDS OF ADJACENT CORES BEING SPACEDFROM EACH OTHER TO FORM GAPS SUBSTANTIALLY IN ALIGNMENT WITH SAIDAPERTURES FOR FORMING MAGNETIC FIELDS FOR INDEPENDENTLY DEFLECTING EACHOF SAID ELECTRON BEAMS PASSING THROUGH SAID APERTURES IN SAID FOCUSINGELECTRODE AND ANODE AND THEN THROUGH SAID GAPS.